Manufacture of ammonium sulfate from refinery wastes



Aug. 11, 1953 vD. A. H. OLSON 2,648,594

MANUFACTURE OF AMMONIUM kS.]I..F`'I`1'; FROM REFINERY WASTES Filed May1o, 1951 DAN A. u. OLSON AGENT .wbb/)kijf Patented Aug. 11, 1953 MANUFACTURE 0F AMMONIUM 'SULFATE FROM REFINERY WASTES Dan A. H. Olson,Huntington Park, Calif., assignor to Socony-Vacuum Oil Company,Incorporated, New York, N. Y., a corporation of New York Application May10, 1951, Serial No. 225,507

11 Claims. l

This invention relates to the manufacture of ammonium sulfate from theammonia produced in the cracking of nitrogen-bearing petroleum fractionsand from the sludge obtained in the treatment of petroleum distillateswith sulfuric acid.

Ammonium sulfate has previously been made from acid sludge by thereaction of ammonia or a strong ammonia solution with the sludge or withan aqueous acid Vsolution obtained by hydrolysis of the sludge. In theseprocesses removal of nitrogen bases and other contaminants has been aserious problem; even though elaborate oil-separation systems have beenemployed, the ammonium-sulfate crystals eventually produced have beencolored, malodorous, and not free of a ytendency to become caked instorage.

The materials withdrawn from catalytic cracking units includeconsiderable quantities of Water which, after condensation, is separatedfrom the hydrocarbons and withdrawn. In the case of a refinery employingnitrogen-rich crude oil, such as California petroleum, this watercontains ammonia in solution, principally as the hydrosulflde,lsulda'and carbonates of ammonium. To a lesser extent, similar wastewater is obtained from the products of thermal cracking units and fromother sources in a refinery. I-Ieretofore, utilization or even disposalof this waste water has been a diicult problem.

In the present process, the waste water is stripped'with steam to yielda vaporous eiiluent consisting of steam with 2% to 3% ammonia, a similarproportion of hydrogen sulfide, and a smaller proportion of carbondioxide. The fouled steam is introduced to a reaction vessel with acidsludge, added oil of low volatility, and a recycled solution of ammoniumsulfate. In the reaction vessel,`the steam (aided by heat fro-m theexothermic reaction) again acts as a stripping medium, removing the morevolatile components and decomposition products of the acid sludge. Asuspension of less volatile oil in a strong aqueous solution of ammoniumsulfate is withdrawn from the reactor. This suspension separates easilyand cleanly under the mildly acid conditions hereinafter specied, andafter separation the oil-free solution of ammonium sulfate is passed tocrystallizing equipment wherein water is evaporated by means of the heatcarried from the reactor.

This process avoids concentration of ammonia beyond the 2%-3% levelfeasible by steam stripping, it avoids preliminary hydrolysis of acidsludge, it simplifies separation of sludge oil from the aqueoussolution,and it yields 'a crystalline 2 ammonium sulfate which is colorless,odorless, and free-flowing.

The drawing is a flow diagram illustrating the process.

Referring to the drawing, the material introduced by line It is thewaste water drawn from various sources in a refinery, carrying insolution ammonia, hydrogen sulfide, carbon dioxide, and minor amounts ofother impurities. In stripping column I I this Water is brought intocontact with steam introduced by line I2 and withdrawn by line I3. Thestripped waste water withdrawn by line I4, which is virtually freed ofits impurities, may be discharged to a sewer or utilized.

The fouled steam in line I3, carrying NH3, H28, and CO2, is introducedto the lower portion of reaction vessel I5, preferably at a plurality ofpoints distributed about the circumference of the vessel. Acid sludgefrom line It, mingled with oil from line I'I, is introduced to thebottom of the reactor. Recycled ammonium-sulfate solution from line I8,together with a small amount of water from line I9, is also introducedto the bottom of the reactor.

The acid sludge in line I6 is the waste product obtained in thetreatment of various petroleum fractions with sulfuric acid. This sludgeis an extremely complex material, containing (among other components)sulfonic acids, sulfuric esters, sulfates of nitrogen bases, water, freesulfuric acid, and entrained oil. The available sulfuricacid content ofthe sludge is ordinarily between 30% and 50%. The sludge is augmented byfrom 5% to. 100% (preferably at least 20%) by volume of oil from lineI'I. This oil should be substantially nonvolatile under the conditionsexisting in the reactor, and it is preferably an aromatic fraction, suchas the cycle stock from a catalytic cracking unit.

The fluids within the reactor are kept in a state of vigorous agitationby the introduced steam, thus insuring effective contact among the oil,gas, and aqueous phases.

The ammonia introduced with the steam reacts with the free sulfuric acidand the sulfates of nitrogen bases, and to some extent with othercompounds of sulfuric acid, to produce ammonium sulfate. The reaction isstrongly exothermic and ordinarily supplies al1 the heat required forthe eventual evaporation of water and crystallization of the product.

The hydrogen sulfide and carbon dioxide pass through the reactorunchanged and are withdrawn by overhead vapor line 20, together withenough steam to maintain the ammonium-sulfate concentration o-f theaqueous phase of the liquid eiuent (Withdrawn by line 2!) at at least35% by Weight and preferably at 45% to 50%, or just less than saturationat the existing temperature. In preferred forms of the process, theamount of steam Withdrawn is approximately equal to the amount of steamintroduced; so the steam also may be regarded as passing through thereactor unchanged.

It is not to be understood that the concentration of the liquid eiiiuentshould be controlled by variation in the quantity of steam Withdrawn. Itis preferable to maintain a constant pressure in the reactor. Thispressure is chosen with a view to the general level of ammonium-sulfateconcentration Which is preferred, but actual control of theconcentration is effected by variation of the small amount of make-upwater added by line YI9 or, if necessary, by applying supplementary heatto the system in a manner which will be described.

In addition to the steam, hydrogen sulfide, and carbon dioxide, linewithdraws the volatile products of the sludge decomposition, which mayamount to half of the oily materials yielded by the process. This factcontributes greatly to the success of the process, since the volatileoil includes Ythose substances (suchas the lower, Amore active `nitrogenbases) which have been the Vmost harmful in previous processes formanufact-ure of ammonium sulfate from acid sludge. The immediate removalof these substances at the time of the reaction is simple andunexpectedly effective, Whereas their removal at a later stage of theprocess could be achieved only with diiiiculty. If substantiallycomplete removal of these substances from the ammonium-sulfate solutionis not achieved, the crystals produced are malodorous and Votherwise ofpoor quality.

Also, vvthe Withdrawn vapors include such sulfur dioxide as may bederived from the acid sludge.

The less volatile oils from the acid sludge, assisted by the oil addedfrom line f1, form a liquid oil phase which is capable of separatingreadily and ,cleanly from the aqueous solution, provided that alkalineconditions are avoided. Consequently, the harmful icy-products of thereaction are removed from 'the aqueous solution either by ebullition orby solution in the oil phase. Similar purification of theammonium-sulfate solution, which is essential to the recoveryof a goodquality crystalline product, has been achieved in the past only lbyelaborate combinations of stripping, filtration, extraction, etc.

The ow of vacid sludge to the reactor is controlledto maintain theacidity of the contents -of the reactor (as measured in the aqueousphase of the liquid effluent) between the limits 0.05% and 1.5% freesulfuric acid by Weight, preferably between the limits 0.1% and 0.5%.

The vapors 'in line 20 are conveyed to condenser `22 and separator 23.From the latter, 'gas is withdrawn by line 24, oil by line 25, and Waterby line 26. The gas consists mainly of hydrogen sulfide with smalleramounts of water vapor, carbon dioxide, and sulfur dioxide; thismaterial may be combined with other supplies of hydrogen sulfide formanufacture into sulfur and sulfuric acid. The Water, which is somewhatcontaminated with acidic 'gases and nitrogen bases, is `returned tostripper Il by pump 21. The oil, which may be utilized'in various Ways,is conducted to storage.

Y, Line A`2li is provided with back-pressure regular 28 which, togetherwith the valves of the conventional'interfa'ce controllers in separator23, main- 4 tains constant pressure in line 20 and in reactor Theabove-mentioned solution of ammonium sulfate bearing in suspension oilof low volatility overflows from the liquid surface Within reactor l5and is conveyed to separator 29 by line 2l. This separator includesstandpipe 3'0, the upper end of which communicates with vapor line 20`.by means of line 3 l, to maintain equalized pressure in the reactorand in the separator. `Separated oil is Withdrawn by line 32 andconducted to storage, While separated ammonium-sulfate solution is takenbyline 33 and conveyed to the crystailizing vequipment generallyindicated at 34.

The crystallizer, which is of known design, includes crystal 'suspensionbasket 35, vaporizing chamber `36 communicating with the bottom ofthebasket by barometric leg 31, and circulating pipe '38, which isprovided with pump 39 and heater 40. Since the heat from reactor I5normally supplies all the heat needed'to operate Athe crystallizenheater 40 is ordinarily used only Sto facilitate starting the process;however, -theheater also serves as a stand-by to Vproviifle supple;mentary heat in the event that -it is needed.

The ammonium-sulfate solution from separator 29 is conveyed to vthe'intake vof pump 39, Where it is mixed with some of Vthe cooler, vsat-'-urated solution from basket 35, and the combined stream is pumped intovaporizer 36 Where water vapor vis flashed off by 'reduction of pressureLtoa subatmospheric level. 'The supersaturated solution of ammoniumsulfate which is produced by this evaporation `flows down throughbarometiic leg 31 to the bottom of basket '35 v1wherein crystal growthoccurs. lThe larger lcrystals-settle tothe bottom of the basket, while.smailr ones lremain suspended by the upvvard'ii'ow of liquid 'in 'thebasket.

In addition to the solution taken `-from the basket by pump 39, arecycle stream -is withdrawn from the upper portion vof the 'basket byoverow and is conveyed by line IH to mothereliquor tank `42.

A slurry of fully grown ammonium-sulfate crystals is withdrawn from thebottom of basket 35 `by pump 43 Vand conveyed by line M to oentri'fuge45. 'In the centrifuge, which is also of known design, the excesssolution' is `whirled ou, the crystals are washed with la small volumefof Water or ammonia solution, and the crystals are finally dried by astream of warm air ariddisf charged. The liquid from the centrifugei-scon-l veyed to tank l2 by line 46.

The low pressure in v'apori'zii'ig fc'haniber '3621s maintained bycondenser 411, 'wlfii'cli with(irait/*isV and lquenes water vapor 'fromthe top of fthe vaporizer. l K Y A stream of ammonium-sulfate vsciutioriis pumped from tank `42 into "line I8 and returned to reactor l5.recycle is to provide "'a 'medium for transmitting heat from the reactorto the crystallizer. riti" the comparatively small volume of `'freshlycreated ammonium-sulfate solution'vvere relieilu'pon for carrying theheat, it would be necessary to "op erate the reactor at excessivelyrhigh temperature 'and pressure, 'but if the aqueous .eiuent from thereactor is augmented by the recycle., only moderate temperature andpressure are required. Also, the recycle serves to stabilize .ammoniumsulfate concentration, acidity, and other conditions in the reactor. l I

The reactor is operated at the boiling point 4of the strongammonium-sulfate l'solution Vexisting The primary function y"of this'therein at the chosen pressure, which should be somewhat greater thanatmospheric. Since the aqueous solution must be at least 35% ammoniumsulfate, and since it is scarcely feasible to operate the reactor atless than atmospheric pressure, the minimum reaction temperature is 217F. With the somewhat higher concentration and pressure ordinarilypreferred, the reaction temperature is 240 F. or more. The exothermicreaction between ammonia and the acid sludge supplies all the heatnecessary to raise the sludge, oil, recycled liquor, and make-up waterfrom lines I6 to I9 inclusive to that temperature. Of these materials,the sludge, oil, and make-up water ordinarily have initial temperaturesat about the atmospheric level, while the recycle stream may be at about150 F. The steam in line I3 is at a temperature somewhat higher thanthat of the reactor; however, little or none of this steam is condensed,and the heat available from its temperature drop is at least balanced bythe heat required to vaporize the Volatile oils from the sludge.

The heat of reaction is, in fact, a little more than suilicient toeffect the necessary evaporation of water and crystallization ofammonium sulfate in the crystallizer and to make up for customary heatlosses. It is for this reason that ladditional water to be evaporated issupplied from line I9. Other methods of removing excess heat arefeasible, but do not provide such con- Venient and accurate control ofthe heat balance and the ammonium sulfate concentration.

If the requirements for heat energy were the only consideration, itwould not matter how the total withdrawal of Water vapor is proportionedbetween the overhead from reactor I5 and the overhead from vaporizer 36.However, in order to obtain the best purication of the ammonium-sulfatesolution, it is necessary that the stripping e'ect in the reactor be ata maximum and that the concentration of ammonium sulfate in the reactorand in separator 29` be as great as possible without danger of prematurecrystallization of ammonium sulfate. For both reasons, it is preferablethat the withdrawal of steam from the reactor be at the highest ratewhich can be employed without approaching too closely to a saturatedsolution of ammonium sulfate in the reactor and without requiring theaddition of more water from line I 9 than can be evaporated by theavailable excess heat. Concentrations down to about 35% by weightammonium sulfate in the aqueous phase of the reactor effluent can beemployed successfully, but below that level the retention of malodoroussubstances in the aqueous solution increases sharply, with the resultthat the crystalline product is objectionable.

In a specific example of the process, reactor I5 is a closed, stainlesssteel vessel of 275 barrels capacity and containing a liquid body 16feet in depth. The crystallizer and centrifuge are of known design, andthe condensers, separators, valves, pumps, etc. are standard equipment,well known in petroleum refineries and elsewhere.

With the plant running at capacity, line I3 carries about 11,000 poundsper hour of fouled steam containing 2.6% ammonia, at a temperature of256 F. and pressure of 20 pounds per square inch gauge. The flow of acidsludge in line I6 is controlled to maintain the free acid content of theaqueous solution withdrawn from the reactor within the limits 0.1% to0.5% by weight, which results in the consumption of a 6 little over2000l pounds per hour of sludge of 41% sulfuric-acid content and 14%Water content. Line I1 adds 25% by volume, with respect to the sludge,of cycle stock from a catalytic cracker, which is a highly aromaticfraction having an initial boiling point of 420 F.

Line I8 carries about 91601 pounds per hour of recycled 47.5%ammonium-sulfate solution at a temperature of F. The quantity of wateradded by line I9, which is varied to maintain the concentration of theaqueous ammoniumsulfate solution withdrawn from the reactor at close to50% by weight, runs about 330 pounds per hour.

Back-pressure controller 28 is set at 5 pounds' per square inch gauge,which, because of pressure drop in the intervening equipment, results ina pressure of 7 pounds per square inch gauge and a temperature of 243 F.in the top of reactor I5.

With the exceptions of the withdrawal of the recycle stream by line 4Iand the usual nonuse ofheater 40, the crystallizer and the centrifugeare operated entirely in the conventional manner. The pressure invaporizer 35 is maintained at about 2.9 pounds per square inch absolute.

The product of the above-described plant, which amounts to about 13.4tons per day of ammonium sulfate at full capacity, has been found toconsist of colorless, odorless, free-owing crystals having averagenitrogen content of 20.91%, moisture content of 033%, and free sulfuricacid content of 018%.

I claim as my invention:

l. A method of manufacturing ammonium sulfate which includes:continuously introducing to a reaction zone ammonia, steam, and amaterial containing sulfuric acid, oil, and oilsoluble contaminants;withdrawing from said reaction zone a suspension of aqueousammoniumsulfate solution and liquid oil, said liquid oil including theless volatile portion of said contaminants; withdrawing from saidreaction zone steam with vapors of volatile contaminants, saidwithdrawal of steam being sufficient in amount to yield concentration ofat least 35% ammonium sulfate by Weight in said withdrawn aqueoussolution; maintaining sufcient liquid Water in said reaction zone toprevent crystallization of ammonium sulfate therein; and separating saidwithdrawn aqueous solution from said liquid oil.

2. A method as defined in claim 1, including the introduction to saidreaction zone of an oil substantially nonvolatile at the temperature andpressure of said reaction zone.

3. A method as defined in claim 1, in which said withdrawal of steam iscontrolled by maintenance of constant pressure in said reaction zone andin which minor variations of ammonium-sulfate concentration of saidwithdrawn aqueous solution are controlled by introduction of a variablequantity of Water to said reaction zone.

4. A method as defined in claim 1, in which said separatedammonium-sulfate solution is partially evaporated to eiiectcrystallization of ammonium sulfate, and in which at least a portion ofthe ammonium-sulfate solution remaining from said evaporation andcrystallization is recycled to said reaction zone.

5. A method of manufacturing ammonium sulfate which includes:continuously introducing to a reaction zone fouled steam includingammonia, and oil-bearing acid sludge derived from the treatment ofpetroleum fractions withY sulfuric acidi;- withdrawing from saidreaction zcnea suspension of aqueous ammonium-sulfateA solution and.liquid oil,- withdrawing from said `Areaction zone steam withcontaminants including volatile components and decomposition products ofsaid acid sludge, said withdrawal of vsteam being suiiicient in amountto yield `concentration of at least 35% ammonium sulfate by weight insaid withdrawn aqueous solution; maintaining fsuiiicient liquid water insaid reaction zone to prevent rcrystallization of' ammonium sulfatethereim'and separating said aqueous solution from said liquid oil.

'-6. A method as dened in Iclaim 5, including the introduction to saidreaction zone 0i an oil substantially nonvolatile at the temperature andpressure of said reaction zone.

v'i'. kA method Aas defined in claim 5,- in which said Withdrawal ofsteam is controlled by Ina-ini tenance of constant pressure in Vsai-dreaction zone and vin which minor variations of ammoninna-'sulfateconcentration of said withdrawn aqueous solution are controlled oyintroduction of avariable quantity or water .to said react-ion zone. v

8. A method as defined in claim 5, in which said`- separatedammonium-sulfate `solution is partially evaporated to effectcrystallization of ammonium sulfate, and in which at least a portion ofthe ammonium-sulfate solution remaining from y'said evaporation andvcrystallization is recycled to said reaction zone.

9. A method as defined in claim 5, :in which the proportion of said acidSludge With respect to said ammonia is controlled to maintain the freesulfuric-acid content of said withdrawn aqueous solution within thelimits 0.05% and 1.5% by weight.

10A method of manufacturing Iammonium sulfate which includes:continuously introducing to a stripping zone jsteam andpetroleumrefinery Waste water containing ammonia; withdrawing from saidstripping zone steam fouled .with gaseous substances including ammonia;introducing to a reaction zone said fouled steam and oil-bearing acidsludge lderived yfrom the treatment of petroleum fractions with sulfuricacid; withdrawing from said reaction zonea suspension of aqueousammonium-sulfate solution and liquid oil; withdrawing .from said rc--action .zone .steam with contaminants including volatile components anddecomposition products of Said acid sludge, said withdrawal of steambeing suicient in amount -to yield concentration of at least 3.5%ammonium sulfate by weight in said withdrawn aqueous solution;maintaining sufficient liquid Water in said reaction zone to-preventcrystallization of ammonium sulfate therein; and separating said aqueoussolutio from said Aliquid oil. f l

1l. A method of manufacturing ammonium sulfate which includes:continuously introduc# ing .to a reaction zone ammonia, steam, an oilsubstantially nonvolatile at the temperature and pressure of saidreaction zone, and a material containing sulfuric acid and oilsolublecontaminants; withdrawing from vsaid reaction zone-a suspension ofaqueous ammonium-sulfate s olution and liquid oil, zsaid liquid oilincluding the less volatile portion of said-contaminants; Withdrawingfrom said reaction zone steam with vapors of lvolatile contaminants,said withdrawal of steam being sufcient in amount to yield concentrationVof at least 35% ammonium v.sulfate by weight in said Withdrawn aqueoussolution; maintaining suflicient liquid water in said Yri?- action zoneto prevent crystallization of ammonium sulfate therein; Yand separatingsaid Withdrawn aqueous solution from said liquid oil.

:nur A. H. oLsoN.

References Cited in the ille of this patent UNITED STATES PATENTS

1. A METHOD OF MANUFACTURING AMMONIUM SULFATE WHICH INCLUDES:CONTINUOUSLY INTRODUCING TO A REACTION ZONE AMMONIA, STEAM, AND AMATERIAL CONTAINING SULFURIC ACID, OIL AN OILSOLUBLE CONTAMINANTS;WITHDRAWING FROM SAID REACTION ZONE A SUSPENSION OF AQUEOUSAMMONIUMSULFATE SOLUTION AND LIQUID OIL, SAID LIQUID OIL INCLUDING THELESS VOLATILE PORTION OF SAID CONTAMINANTS; WITHDRAWING FROM SAIDREACTION ZONE STEAM WITH VAPORS OF VOLATILE CONTAMINANTS, SAIDWITHDRAWAL OF STEAM BEING SUFFICIENT IN AMOUNT TO YIELD CONCENTRATION OFAT LEAST 5% AMMONIUM SULFATE BY WEIGHT IN SAID WITHDRAWN AQUEOUSSOLUTION; MAINTAINING SUFFICIENT LIQUID WATER IN SAID REACTION ZONE TOPREVENT CRYSTALLIZATION OF